Creeping Flashover Characteristics Research Articles

Research on Creeping Flashover Characteristics of Nanofluid-Impregnated Pressboard Modified Based on Fe₃O₄ Nanoparticles under Lightning Impulse Voltages.

Creeping flashover of mineral-oil-impregnated pressboard under impulse stress is a common insulating failure in oil-immersed transformers, arousing increasing attention. Recent studies have shown that the breakdown strength of transformer oil under positive lightning impulse voltage can be significantly improved through nanoparticles-based modification, and Fe3O4 has shown the best improvement in breakdown strength compared to other nanoparticles that have been used. This paper presents the creeping flashover characteristics of pure oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) based on Fe3O4 nanoparticles under positive and negative lightning impulse voltages, respectively. It was found that NIP possessed higher resistance to creeping flashover than OIP. The relative permittivities of oil and oil-impregnated pressboard before and after nanoparticles-based modification were measured, and the results revealed that the addition of nanoparticles led to a better match in relative permittivity between oil and oil-impregnated pressboard, and a more uniform electric field distribution. Furthermore, the shallow trap density in NIP was obviously increased compared to that of OIP through the thermally stimulated depolarization current (TSDC), which promoted the dissipation of surface charges and weakened the distortion of the electric field. Therefore, the creeping flashover characteristics of oil-impregnated pressboard were greatly improved with Fe3O4 nanoparticles.

Effect of the surface roughness of epoxy resin on its creeping flashover characteristics in C4F7N-CO2 gas mixtures

Epoxy resin samples were processed by one direction and multi-directions polishing methods in this research. The contact angles of the samples, the AC/DC flashover voltage in C4F7N/CO2 gas mixtures and the charge dissipation rate of the polished samples were measured. The results show that the contact angle of the polished epoxy resin sample increases. In the gas mixtures, the surface roughness modification of the epoxy resin under different voltage types is proposed. According to the charge dissipation rate, the development mechanism of creeping flashovers under different voltage is revealed. Different dissipative properties ultimately enhance the creeping discharge voltage of the samples by suppressing electron secondary electron emission. This paper offers a basis for insulation design in the C4F7N/CO2 gas mixture.

Influence of TiO2 nanoparticle size on creeping flashover property of transformer oil-impregnated pressboards

Nanoparticles have exhibited great potential in improving insulating property of liquid and solid dielectrics. To explore their modification mechanism on transformer oil-impregnated pressboards, TiO2 nanoparticles with different diameters of 5nm, 10nm, and 15nm were synthesized and used to prepare transformer oil-based nanofluids. The creeping flashover characteristics of both pure oil-impregnated paperboards (OPs) and nanofluid-impregnated pressboards (NPs) were examined under lightning impulse and AC voltages. It was found that the creeping flashover property of NPs is significantly improved with the decreasing of nanoparticle size. Especially, it is enhanced by 2.44 times under positive lighting impulse as nanoparticle size reduced from 15 nm to 5 nm. The results of space charge decay and trap characteristics reveal the decrease of nanoparticle size can lower trap depth and greatly enhance the space charge dissipation rate, leading to more uniform electric field distribution at the interface between nanofluid and pressboards and higher creeping flashover property.

Effect of nanoparticle shapes on creeping flashover characteristics at the interface of nanofluid-impregnated pressboard

Recent studies have shown that the modifications to nanofluid-impregnated pressboards by different shapes of nanoparticles are different. To investigate the effect of nanoparticles shapes on creeping flashover characteristics at the interface of nanofluid-impregnated pressboard (NP), creeping flashover behavior of spherical nanoparticle fluid/pressboard (NSFP) and nanorod fluid /pressboard (NRFP) were compared to that of oil/pressboard (OP) which was used as a reference. Creeping flashover experiments under AC and positive and negative impulse voltages were carried out. Results show that the modifications by spherical and rod nanoparticles on creeping flashover strength are distinct and different: negative creeping flashover voltages of NSFP and NRFP are increased up to 32 and 15% respectively, and the positive ones are separately improved as high as 15% and 5%. Whereas, experiments under AC voltage reveal quite a different trend: creeping flashover voltage of NSFP and NRFP are almost increased to the same extent, nearly 18%, while partial discharge inception voltage improvement in the increment of the former is 5.6 times larger than that of the latter. Charge behaviors at oil/pressboard interfaces were displayed by thermally stimulated depolarization current method. Space charge accumulation at the surface of NSFP is much less than that of NRFP and the dissipation rate of the former is faster, due to a larger trap density and a lower trap energy level, which weakens electric field distortion and results in the improvement of creeping flashover strength. The underlying mechanism is that spherical nanoparticles have a specific surface area 1.3 times as large as that of nanorods at the same concentration, and it is a source of shallow traps.

Creeping flashover characteristics improvement of nanofluid/pressboard system with TiO2 nanoparticles

Creeping flashover easily occurs at the interface between oil and pressboard in transformer and thus results in outage of power transmission system. Investigations have shown that creeping flashover characteristics at oil/pressboard interface can be improved by the addition of TiO2 nanoparticles, but the mechanism is still not thoroughly known. In this work, creeping flashover performance at nanofluid/pressboard interface modified by different sizes of nanoparticles were studied and the mechanism was presented as well. Nanofluids with the same concentration but with different sizes of TiO2 nanoparticles were prepared, and pressboards impregnated with them were prepared as well. After that, their creeping flashover characteristics were measured and compared. Nanoparticle’s size affected the creeping flashover performance along oil/pressboard greatly under both AC and lightning impulse voltages. The highest creeping flashover voltage can be enhanced by as high as 12.2% and 32.0% respectively. The underlying electric field distribution and charge transportation behaviors were analyzed to demonstrate the influence of nanoparticle’s size. By the addition of nanoparticles with a smaller size, the dielectric constant of nanofluid was increased closer to that of the pressboard, thus they were matched better. Moreover, charge was easier to dissipate from the oil/pressboard interface and electric field distortion at the interface was consequently reduced. Therefore, the electric field was more like a uniform field and the forward development of flashover was more difficult, leading to a better performance of creeping flashover of oil-impregnated pressboard.

Nanoparticle effects on creeping flashover characteristics of oil/pressboard interface

Surface creeping discharge at solid-liquid interface is regarded as one of the reasons for oil-immersed transformers failure. In order to restrain the surface creeping discharge, we investigated the effects of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles on creeping discharge and flashover characteristics of the oil/pressboard interface under AC and impulse voltages. Partial discharge and creeping flashover tests of oil/pressboard (OPs) and nanofluid/- pressboard (NPs) were carried out. The results show that TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles can improve both partial discharge inception voltage (PDIV) and creeping flashover strength of oil-impregnated pressboards. Thermally Stimulated Depolarization Current (TSDC) and Electrostatic probe techniques were used to measure space charge behaviors of oil/pressboard before and after modification of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles. It reveals that the space charge dissipation rate at the surface of NPs is much faster than that of OPs. Moreover, TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles can greatly increase the shallow trap density and lower the shallow trap energy level of oil-impregnated pressboard. It is believed that electrons may be repeatedly trapped and de-trapped by shallow traps in NPs, which can reduce the accumulation of space charges and result in improving the creeping flashover strength of oil/pressboard interface.

Anomalous creeping flashover characteristics in N/sub 2//SF/sub 6/ mixed gas under single pulse voltage

Creeping flashover characteristics for the needle electrode-plane electrode filled with N/sub 2//SF/sub 6/ gas mixtures have been investigated. In the case of the needle-plane configuration, the flashover voltage was enhanced by an admixture of SF/sub 6/ into N/sub 2/. On the other hand, by the insertion of a solid dielectric barrier between the needle and the plane, only the negative creeping flashover voltage was reduced drastically by the admixture of SF/sub 6/ gas into N/sub 2/ gas, and a highly emissive region at the top of a creeping corona was found in N/sub 2//SF/sub 6/ gas mixture. This behavior is strongly affected by the creeping corona extension process, depending on the creeping distance and the gas pressure.

Creeping flashover characteristics in (N2/SF6) gas mixture under pulse voltage

Creeping flashover characteristics in (N2/SF6) gas mixture under pulse voltage

Creeping flashover characteristics in (N2/SF6) gas mixture under pulse voltage

The effect of a barrier between a needle electrode and a plane one in an (N2/SF6) gas mixture on creeping flashover was investigated using a microsecond pulse voltage. The SF6 gas content was varied from 0% to 100%, and the gas pressure from 0.1 MPa to 0.3 MPa. The flashover voltage increased with increasing SF6 gas content for a positive needle electrode. For a negative needle electrode, excepting the total pressure of 0.1 MPa, at which similar flashover characteristics were obtained to the positive case, a considerable decrease in flashover voltage was found in the case of a mixture of a few percent SF6 in (N2/SF6) gas mixture at elevated total pressures. The corona behavior on the barrier in (N2/SF6) gas mixture was investigated by means of a high-speed digital framing camera. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 1–9, 2000

Creeping flashover characteristics in (N 2 /SF 6 ) gas mixture under pulse voltage

Creeping flashover characteristics in (N _<b>2</b> /SF _<b>6</b> ) gas mixture under pulse voltage